The present invention relates to a device for dispensing a fluid, and more particularly a device for dispensing a liquid medicament contained in a hermetically closed container.
In the field of devices for spraying a medicament, and in particular for single-dose devices or for two-dose devices, numerous problems arise. In particular, the most critical problem that is to be solved concerns the stability of the liquid medicament contained in the container of the device.
Between the moment the liquid is put into place in the container of the device, and the moment when it is dispensed, i.e. during the storage period, the liquid tends to evaporate or can be contaminated by external agents such as bacteria, or can be oxidized by oxygen. With certain medicaments, that can cause it to lose its effectiveness completely.
To solve that problem, two types of systems have been used for the most part:
A first type of system comprises a container whose opening is closed by a membrane, said membrane being pierced or torn by appropriate means when the device is actuated. Such systems are described, in particular, in documents EP-0 407 276 and U.S. Pat. No. 4,017,007. The drawback of those membrane devices lies in the fact that the membrane must be applied to the opening of the receptacle with care, thereby requiring a relatively complex assembly step after the container has been filled. Thus, the liquid contained in the container is exposed to possible contamination during the time required for applying said membrane.
In a second type of system, a rubber element used as a pump piston is pierced at the moment of dispenser actuation by a needle which is connected to the spray outlet of the dispenser. One such system is described in document FR-2 684 304. In that type of system, which solves the membrane problem, the size of the piston must be such as to enable it to slide relatively easily in the container. In other words, interference between the piston and the container, i.e. the pressure exerted by the piston against the walls of the container, and consequently the area of contact between those two elements, must be as small as possible in order to avoid problems of friction when the dispenser is being actuated, and also to minimize the force required for actuating the dispenser. This characteristic of little interference means that the amount of protection given against evaporation under certain conditions is limited, for example when storage takes place at high temperatures, and it can also allow the substance to be contaminated, e.g. by the penetration of oxygen.